A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface. Because the read/write head flies so close to the surface of the magnetic-recording disk, the components within the HDD may be sensitive to moisture, contaminants, and other impurities and imperfections within the protective enclosure of the HDD.
To improve the operating conditions of the components within the HDD, a chemical may be placed within the protective enclosure of the HDD. This chemical may provide a vapor with beneficial properties (a “beneficial vapor”) to improve the operation of the components within the HDD. For example, the beneficial vapor may help prevent corrosion, improve lubricity, or suppress the formation of smears. When a beneficial vapor is used within the interior of the HDD, it is desirable to regulate the concentration of the beneficial vapor to provide the most benefit to the components of the HDD. If the concentration of the beneficial vapor within the HDD is too great, the mix of gasses within the protective enclosure of the HDD may become saturated with the beneficial vapor, thereby causing the beneficial vapor to condense. The condensation of the beneficial vapor may decrease the benefit derived from the beneficial vapor and possibly interfere with the proper operation of the components of the HDD.
Modern HDDs have a very thin overcoat and lubricant layers as well as very thin or even absent protective layers on the read and write heads. To protect high performance drives against corrosion and other negative outcomes, it is desirable to control the relative humidity within the drives. This has been accomplished in certain HDDs through the use of desiccants.